1. Field
The apparatus and method described in this patent specification relate to an optical apparatus, in particular, an optical apparatus using a light source in the form of a micro-light source array such as an LED (light emission diode) array or an EL (electroluminescence) array, etc., employed in the optical writing-in unit of a scanner, etc., or in an electrophotographic printer, a digital copying machine, a facsimile device, etc.
2. Background Technology
In recent years, there has been an increase in the use at home or in small businesses of office equipment that previously was found mainly in larger firms. As a result, there has been an increase in the demand for compact and low-cost office equipment such as electrophotographic printers, etc., that still provide high resolution and high print or copy quality.
One example of such apparatus is an LED printer, which is an electrophotographic printer employing an LED (light emitting diode) array comprising a large number of LEDs. Because a printer of such type uses a fixed writing light source incorporating the LED array, the apparatus itself can be more compact than a comparable raster scanning printer employing a semiconductor laser (laser diode) and a mirror scanning system. In addition, the LEDs in an LED printer can write in parallel (simultaneously) and thereby make it simpler to increase writing speed.
When the light source is an LED array, the light from the individual LEDs needs to be delivered onto the light-receiving surface (e.g., photosensitive or photoconductive surface) at high resolution and high efficiency. Furthermore, in order to make the apparatus more compact, the distance between the light source (LED array) and the light-receiving surface needs to be minimized. For this reason, a suitable focusing optical system is required. A rod lens array composed of bundled plural rod lenses has been used for such focusing in many LED printers.
FIG. 5 illustrates a structure discussed in the published specification of Japanese Laid-open Patent Publication No. 7-108709/1995, and is an example of an optical apparatus employing such a rod lens array in which light rays emitted from each of LEDs 102 in an LED array 101 (comprising a number of LEDs 102 arranged in a row extending in a direction perpendicular to the drawing sheet) are projected onto a photosensitive surface 105 by the focusing action of a corresponding rod lens 104 in the rod lens array 103 (which also comprises a number of lenses 104 arranged in a row extending in a direction perpendicular to the drawing sheet). As a result, a fine spot image is focused on the photosensitive surface 105. The rod lens array 103 forms the focusing optical system 106.
FIG. 22 is a similar cross-sectional view of the proposal discussed in the same Patent Publication, and shows that the light rays emitted from an LED 302 in an LED array 300 are projected onto a photosensitive surface 306 by the focusing action of a corresponding rod lens 304 in a rod lens array 103 to thereby produce a finely focused light spot at photosensitive material 306.
Another use of an LED array in an optical apparatus is illustrated in FIGS. 6 and 23, and is discussed in the published specification of Japanese Laid-open Patent Publication 8-1998/1996. In FIG. 6, light rays emitted from an LED 112 in an LED array chip (LED array) 111 are guided to a photosensitive surface facing or contacting an optically opaque block 114 through a corresponding light guiding path 113 in block 114, which is mounted on the LED array chip 111. In FIG. 23, light rays emitted from an LED 312 in an LED array 310 are guided to a photosensitive surface facing or contacting an optically opaque layer 314 through a corresponding guiding path 316 in the form of a light pipe formed in layer 314.
The rod lenses of a rod lens array system of the type illustrated in FIGS. 5 and 22, transmit light relatively efficiently to the photosensitive surface 105. However, because the light emission angle of an LED 102 in the LED array 101 is inherently wide and includes much more than the facing area of the corresponding rod lens 104, much of the light energy emitted from an LED does not reach its rod lens 104. As a result, there is poor utilization efficiency of the light energy that an LED emits. Consequently, if a predetermined amount of light energy or intensity is required at the photosensitive surface 105, it is necessary to emit much more energy or intensity from the LED, with a corresponding need for high drive electric current to the LED 102 and a corresponding undesirable heating of the LED 102.
The LED arrays of the type shown in FIGS. 6 and 23 also have a relatively poor light energy utilization and, in addition, fail to provide a light focusing function and, therefore, unless the photosensitive surface is brought very close to or in contact with the optical system (the layer 114), the light image formed on the photosensitive surface is out of focus, resulting in poor resolution.
The system and method disclosed in this patent specification are designed to overcome these and other deficiencies in known approaches and to provide improvements in delivering light energy to a light receiving surface efficiently and effectively.
To this end, the disclosed system and method use a light source such as an LED or an EL array in an arrangement that increases the light energy utilization as compared with known systems and methods, while retaining significant benefits of such known systems and methods. One aspect of the disclosed approach is to use technology similar to that used in the integrated circuit (IC) technology to form an LED at the bottom of a recess whose walls serve to direct much more of the light energy from the LED to an element such as a rod lens that guides or some other focusing or light guiding system that in turn delivers the light energy to a light receiving surface.